# The Naked Scientists Forum

### Author Topic: Understanding hammerthrow forces (no friction with ground)  (Read 1771 times)

#### trytyutry

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##### Understanding hammerthrow forces (no friction with ground)
« on: 12/08/2014 18:11:48 »
If I understand it correct during hammerthrow an athlete muscles cause Fcentripetal force on a ball and ball cause reaction Fcentrifual force on athlete.
The athlete also cause Frotation on ball by rotating his body and ball cause Freaction on athlete.

What would happen if athlete would try to throw the heavier ball than himself being in the air - by rotating his body  (no friction between athlete and the earth - I mean the athlete and the ball are both in the air) ? Would it be even possible or would athlete rotate himself around ball(cause ball is heavier) ?

#### RD

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##### Re: Understanding hammerthrow forces (no friction with ground)
« Reply #1 on: 12/08/2014 19:53:29 »
Scottish hammer throwers are anchored with shoe spikes stabbed into the turf ...

#### evan_au

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##### Re: Understanding hammerthrow forces (no friction with ground)
« Reply #2 on: 13/08/2014 11:09:33 »
Assuming the hammer is initially accelerated with the athlete standing on the ground, frictional forces allow the ball to get moving.
• If the hammer and thrower then both become airborne, they will rotate around their common center of gravity, with the rope in tension.
• If the thrower releases the rope, the thrower and ball will then separate in opposite directions, and fall to the ground.

If the athlete and hammer are in free fall, far from other objects:
• The athlete will be able to get the hammer moving by pulling on the rope.
• The athlete would not be able to get the hammer moving as efficiently as on Earth by swinging it around and around, as the athlete will start to spin in the opposite direction
• Releasing the rope would allow the hammer and athlete to separate in opposite directions, but both will now be spinning.

I expect that:
• A hammer lighter than the athlete will go further than one that is heavier than the athlete.
• The hammer will go further if the athlete is able to maintain ground contact for longer.
« Last Edit: 13/08/2014 11:14:37 by evan_au »

#### trytyutry

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• Posts: 4
##### Re: Understanding hammerthrow forces (no friction with ground)
« Reply #3 on: 14/08/2014 19:21:07 »
Isn't it actually that forces are opposite but rotation is in the same direction? Cause it would look something like

and if I am not wrong the opposite rotation direction looks like that (first object right; second object left)

#### The Naked Scientists Forum

##### Re: Understanding hammerthrow forces (no friction with ground)
« Reply #3 on: 14/08/2014 19:21:07 »